Comcast is mounting an aggressive defense of its BitTorrent blocking, telling the Federal Communications Commission that its decision to slow some file transfers are absolutely necessary to keep its network operational and have been mischaracterized by critics.

The broadband provider told the FCC that it delays only peer-to-peer uploads--at times when a download is not taking place as well--and then only during periods of peak network congestion.

Here's an excerpt from Comcast's filing on Tuesday:

Comcast's network management
practices (1) only affect the protocols that have a demonstrated history of generating excessive
burdens on the network; (2) only manage those protocols during periods of heavy network
traffic; (3) only manage uploads; (4) only manage uploads when the customer is not
simultaneously downloading (i.e., when the customer's computer is most likely unattended)
("unidirectional sessions" or "unidirectional uploads"); and (5) only delay those protocols until
such time as usage drops below an established threshold of simultaneous unidirectional sessions.

Although network management practices must respond to new technological
developments and necessarily change over time, Comcast to date has not found it necessary to
manage traffic associated with downloads, or bidirectional traffic (i.e., uploads that occur at the
same time a customer is downloading). P2P file uploads that are underway before the network
management threshold is reached are not interrupted, and neither bidirectional file transfers nor
downloads--including new ones--are affected. This action is nothing more than the system
saying that it cannot, at that moment, process additional high-resource demands without
becoming overwhelmed, just as a traffic ramp control light regulates the entry of additional
vehicles onto a freeway during rush hour. One would not claim that the car is "blocked" or
"prevented" from entering the freeway; rather, it is briefly delayed, then permitted onto the
freeway in its turn while all other traffic is kept moving as expeditiously as possible, thereby
ensuring order and averting chaos. This is an appropriate analogy to Comcast's management of
P2P unidirectional uploads.

This is the most detailed description yet of what Comcast is doing--as recently as last fall, it was still unclear exactly what kind of BitTorrent or other filtering was taking place.

A coalition of liberal advocacy groups including Public Knowledge, along with a parallel request from Vuze, had asked the FCC to stop Comcast from throttling BitTorrent traffic and to declare that the company had violated the FCC's broadband policy principles. They say says consumers can generally use the applications and access the Web sites of their choosing, with an exception for "reasonable network management."

About the author

Declan McCullagh is the chief political correspondent for CNET. You can e-mail him or follow him on Twitter as declanm. Declan previously was a reporter for Time and the Washington bureau chief for Wired and wrote the Taking Liberties section and Other People's Money column for CBS News' Web site.
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